1. Field of the Invention
The present invention relates to a system for sensing relative vertical movement between the wheels of a vehicle and the vehicle chassis or frame, and adjusting the braking force while applying the vehicle brakes to the vehicle wheels in response to that vertical movement.
2. Description of the Prior Art
When brakes are applied to a moving vehicle employing brake fluid in a fluid braking system, braking power is controlled in the first instance by means of a brake peddle or lever. That is, in a fluid braking system a brake fluid reservoir, namely the master brake cylinder, is connected by tubular brake lines to the brake cylinders at each wheel. Increased pressure within the closed brake line system forces the brake calipers toward a rotating disc or the brake shoes toward a brake lining. Pressure is increased in the brake system to cause a mechanical actuation of the calipers or brake shoes by depressing the brake peddle or lever so as to force a certain amount of brake fluid into the brake line, thereby increasing pressure in the line and actuating the brakes.
While the operator of the vehicle can generally determine the appropriate pressure to apply to the vehicle wheel brakes by resistance felt in depressing the brake actuator, there is normally a very rapid fluctuation in the appropriate braking force that should be applied due to relative vertical movement between the vehicle wheels and the frame or chassis of the vehicle. This fluctuation is particularly pronounced when the vehicle is traveling upon a rough surface.
When a brake is applied to a wheel of a vehicle rolling along a perfectly flat surface, the appropriate force to stop the wheel from turning is determined by the coefficient of friction between the area of contact of the vehicle wheel and the surface across which the wheel is traveling. The appropriate braking force is also governed by the vertical weight bearing down upon the wheel.
A simple illustration of this principal is apparent considering the difference in braking force required to stop an unloaded cargo vehicle as contrasted with the force required to stop the same vehicle fully loaded and traveling upon the same surface. Naturally, a much greater braking force is required to bring a heavily loaded vehicle to a halt than to halt the same vehicle traveling in an empty condition.
While a vehicle operator can sense the appropriate braking force to apply under differing conditions of vehicle load, there is another influence on the appropriate braking power to be applied which changes so rapidly that the vehicle operator cannot make timely adjustments to the braking force applied. Specifically, the traction of the vehicle wheel upon the roadway varies rapidly with the vertical movement of the wheel relative to the vehicle frame that occurs due to unevenness of the roadway. This variation of the appropriate braking force to be applied is particularly pronounced when the vehicle is traveling over a rough, bumpy roadway.
When a wheel travels over a depression in the roadway, the wheel normally drops vertically downwardly relative to the vehicle frame or chassis. As the wheel passes over a depression in the road, there is a momentary loss of contact, or at least a reduction of area of contact, between the wheel and the roadway. With the reduction in contact the braking force applied through the brake peddle or lever is momentarily excessive thus resulting in a tendency toward locking of the brake. Conversely, when the wheel crosses a raised bump in the road there is a slight movement of the wheel upwardly in a vertical direction relative to the vehicle chassis or frame. This produces a momentary increase in the vertical load on the wheel so that the applied braking force is momentarily less than optimum.
The small changes in relative movement between the vehicle wheel and the vehicle frame or chassis are far too rapid to allow compensation by the vehicle operator. Consequently, there is excessive wear on the vehicle tires and a loss in stopping force due to the repetitive momentary excessive and insufficient braking forces applied.